Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $114.68   12.600%   $129.1297   $129.13   $129.15   $129.10  
  Purchase #2 $140.40   4.450%   $146.6478   $146.65   $146.65   $146.60  
  Purchase #3 $88.32   4.262%   $92.0842   $92.08   $92.10   $92.10  
  Purchase #4 $250.82   9.744%   $275.2599   $275.26   $275.25   $275.30  
  Purchase #5 $151.61   5.636%   $160.1547   $160.15   $160.15   $160.20  
  Purchase #6 $156.34   5.412%   $164.8011   $164.80   $164.80   $164.80  
  Purchase #7 $59.79   9.461%   $65.4467   $65.45   $65.45   $65.40  
  7 purchase totals = $961.96       $1,033.5241   $1,033.52   $1,033.55   $1,033.50